1. Field of the Invention
The present invention relates to an apparatus and method for driving a liquid crystal display (LCD) device, and more particularly, to an apparatus that improves display quality of the moving image on the LCD screen by removing blurring of the moving images, and method of driving such apparatus.
2. Discussion of the Related Art
Generally, liquid crystal display (LCD) devices adjust light transmittance of liquid crystal cells in accordance with an applied video signal to display an image. An active matrix type LCD device is suitable for displaying a moving image because a switching element is provided for every liquid crystal cell. A thin film transistor (TFT) is used as the switching element of the active matrix type LCD device.
FIG. 1 illustrates a related art apparatus for driving the LCD device. As shown in FIG. 1, the related art apparatus includes an image display unit 2 where a liquid crystal cell is formed in each region defined by first to nth gate lines GL1 to GLn and first to mth data lines DL1 to DLm, a data driver 4 supplies analog video signals to the data lines DL1 to DLm, a gate driver 6 supplies scan signals to the gate lines GL1 to GLn, and a timing controller 8 aligns input data RGB provided externally to the apparatus and supplies the aligned RGB data to the data driver 4. Further, the timing controller generates data control signals DCS to control the data driver 4 and generates gate control signals GCS to control the gate driver 6.
The image display unit 2 includes a thin film transistor array substrate, a color filter array substrate, a spacer, and a liquid crystal material interposed between the two array substrates. The thin film transistor array substrate and the color filter array substrate face each other and are bonded to each other. The spacer uniformly maintains a cell gap between the two substrates. The liquid crystal material is filled in a cell gap formed by the spacer.
The thin film transistor array substrate includes a TFT formed in the region (i.e., liquid crystal cell) defined by intersecting the gate lines GL1 to GLn and the data lines DL1 to DLm. The liquid crystal cells are connected to the TFT. The TFT supplies the analog video signals provided from the data lines DL1 to DLm to the liquid crystal cells in response to the scan signals provided from the gate lines GL1 to GLn. The liquid crystal cell includes common electrodes that face each other where the liquid crystal material is interposed between the two common electrodes, and pixel electrodes that are connected to the TFT. Therefore, the liquid crystal cell functions as a liquid crystal capacitor Clc. In addition, the liquid crystal cell includes a storage capacitor Cst to maintain the analog video signals charged in the liquid crystal capacitor Clc until the next analog video signals are charged therein.
As discussed earlier, the timing controller 8 aligns the input data RGB to desired signals in order to drive the image display unit 2. The timing controller 8 supplies the aligned RGB data to the data driver 4. In addition, the timing controller 8 generates the data control signals DCS and the gate control signals GCS using a dot clock DCLK, a data enable signal DE, and horizontal and vertical synchronizing signals Hsync and Vsync, all of which are externally provided, to control driving timings of the data driver 4 and the gate driver 6.
The gate driver 6 includes a shift register that sequentially generates scan signals (i.e., gate high signals in response to the gate control signals GCS from the timing controller 8). The gate driver 6 sequentially supplies the gate high signals to the gate lines GLs (i.e., GL1 to GLn) to turn on the TFT connected to the each gate lines GLs.
As shown in FIG. 1, signal data ‘Data’ aligned by the timing controller 8 is supplied to the data driver 4. In addition, data control signals ‘DCS’ are provided to the data driver 4 from the timing controller 8. Then, the data driver 4 converts the ‘Data’ into the analog video signals in response to the data control signals ‘DCS’ and supplies the analog video signals to the data lines DLs (i.e., DL1 to DLm). In detail, the data driver 4 selects a gamma voltage having a predetermined level based on a gray level value of the ‘Data’ and supplies the selected gamma voltage to the data lines DL1 to DLm. Then, the data driver 4 inverses polarity of the analog video signals supplied to the data lines DLs in response to a polarity control signal POL.
The related art LCD device has a problem in that response speed is slow due to physical properties of the liquid crystal material, such as an inherent viscosity and an elasticity of the liquid crystal material. Although the response speed of the liquid crystal material may depend on the physical properties and cell gap of the liquid crystal material, it is common for the liquid crystal cells to have a rising time in a range of 20 ms to 80 ms and a falling time in a range of 20 to 30 ms, and this response speed is longer than the one frame period (i.e., 16.67 ms in National Television Standards Committee (NTSC) format).
Accordingly, as shown in FIG. 2, numbers of frame periods may be needed for a voltage being charged to the liquid crystal cell to reach a desired level. In the related art LCD device, the image data in the previous frame period affects the image data in the next frame period, blurring of the moving images appears on the image display unit 2. In addition, viewer perception may also contribute to the blurring of the moving images. As a result, blurring of the moving images causes the degradation of contrast ratio, hence deteriorating the quality of image display on the screen. To prevent the blurring of moving images, an over-driving apparatus is suggested that achieves a fast response speed by modulating data signals.
FIG. 3 is a block diagram illustrating a related art over-driving apparatus. As shown in FIG. 3, the related art over-driving apparatus 50 includes a frame memory unit 52 to store RGB data in a previous frame Fn-1, a look-up table 54 to generate modulated data, and a mixing unit 56 to mix the modulated data from the look-up table 54 with the RGB data in the current frame Fn. The look-up table 54 compares the RGB data in the current frame Fn with a data in a previous frame Fn-1 stored in the frame memory 52. The look-up table 54 lists modulated data R′G′B′ to convert a voltage level of the RGB data in the current frame Fn to a higher voltage level. Accordingly, the liquid crystal material may provide a faster response speed.
As shown in FIG. 4, a voltage level higher than an actual data voltage is applied to the liquid crystal material using the look-up table 54, thus, the blurring of moving images can be reduced. However, since the related art over-driving apparatus 50 generates the modulated data by comparing the data in the current frame with the data in the previous frame, removing the blurring of moving images is limited.